JP2012244244A - Antenna device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an antenna device that can achieve both ensuring electric field intensity of a radio wave and downsizing a body in a coil axial direction.SOLUTION: Transmitters 9 and 10 of a key operation free system of a vehicle includes an antenna unit 15 with a coil 17 wound around the outer periphery of a core 16. The antenna unit 15 is attached to a metal 14 of a vehicle body. A magnetic sheet 18 is disposed between the metal 14 and the antenna unit 15. In an entire length in a longitudinal direction of the magnetic sheet 18, a length from an end portion of the coil 17 in an axial direction (coil axial direction), namely, an allowance L is set at a value of 8-30 mm.

Description

  The present invention relates to an antenna device for wireless communication.

  As is well known in the art, recent vehicles are equipped with an electronic key system that performs key verification using an ID code transmitted wirelessly from an electronic key, and thus various antenna devices are installed on the vehicle body. For example, a bar antenna or the like is used for this type of antenna device (see Patent Document 1). By the way, when the antenna device generates an electric field, if there is a metal nearby, the electric field is consumed by an eddy current generated in the metal, and there is a concern that the electric field strength may be reduced. Therefore, when mounting the antenna device on the vehicle body, it is necessary to dispose the antenna device at a distance from the metal body.

  However, when this measure is taken, it is necessary to secure a mounting space for the antenna device in the vehicle body, and thus there arises a problem that the antenna device cannot be mounted or the vehicle body shape must be changed, for example. . Therefore, by applying a technique (see Patent Document 2 or the like) that can suppress a decrease in the electric field strength of the antenna by arranging a magnetic member between the antenna device and the metal, the above-described problem can be solved. It is being considered.

JP 2008-078899 A JP-A-2005-341027

  By the way, when a magnetic member is provided between the antenna device and the metal body, if a magnetic member having a size covering the entire antenna device is used, the device size including both the antenna device and the magnetic member is used. There was a concern that would become larger. However, this is not a problem of simply reducing the size of the magnetic member, and there has been a demand for an optimal size that can satisfy electric field strength reduction suppression even if the size is reduced.

  An object of the present invention is to provide an antenna device capable of both ensuring the electric field strength of radio waves and reducing the size of the body in the axial direction of the coil.

  In order to solve the above problems, in the present invention, an antenna wire is wound around a high permeability core, and the annular antenna wire becomes a coil of a resonance circuit. A magnetic body capable of absorbing the magnetic field radiated from the coil is provided, and the total length of the magnetic body in the axial direction of the coil is set to a length of 8 to 30 mm away from each end of the coil. The gist.

  According to the configuration of the present invention, since the electric field of the coil passes through the magnetic body, it is difficult for the electric field to go to the antenna installation location side. Therefore, since the loss magnetic field consumed at the antenna installation location side can be suppressed to a small level, it is possible to suppress a decrease in electric field strength. Moreover, when the total length of the antenna device in the axial direction of the coil is set to a length of 8 to 30 mm from each coil end, as a result of the experiment, it was found that a decrease in electric field strength can be sufficiently suppressed. For this reason, since it is possible to suppress a decrease in electric field strength with a magnetic material having a size that is as small as possible, it is possible to achieve both securing the electric field strength of the antenna device and reducing the size of the antenna device in the axial direction of the coil It becomes. Moreover, it leads also to the cost reduction of a magnetic body.

  The gist of the present invention is that the magnetic body is disposed on the antenna device installation site side between the coil and the antenna device installation site. According to this configuration, the electric field output from the coil has more components that pass between the coil and the magnetic body, and the components that pass between the magnetic body and the antenna device installation place are reduced. Therefore, since the electric field that reaches the antenna device installation place can be suppressed, the effect of securing the electric field strength of the antenna device is enhanced.

  In the present invention, the coil is a divided winding in which the group of antenna wires is divided into a main winding and an auxiliary winding, and the antenna wire is further wound around a space formed by the division, thereby The gist is that the number of turns has been increased. According to this configuration, the antenna wire of the coil is divided into windings, and the number of coil turns is increased by further winding the antenna wire in a space formed by winding division. For this reason, even if the electric field is consumed by the magnetic material, the electric field strength can be supplemented, and the effect of securing the electric field strength is enhanced.

  The gist of the present invention is that it includes an antenna unit including at least the coil and a case for housing the antenna unit, and the magnetic body is attached to the back surface of the case. According to this configuration, since the magnetic body is attached to the back surface of the case to which the coil unit is attached, it is possible to make them one unit part. Therefore, it becomes easy to handle the antenna device.

  According to the present invention, it is possible to achieve both securing the electric field strength of radio waves and reducing the size of the physique in the coil axis direction.

The block diagram of the key operation free system of one Embodiment. Sectional drawing which shows the internal structure of a transmitter. The disassembled perspective view which shows the external appearance of a transmitter. The top view which shows the area size of a magnetic material sheet. (A) is a graph which shows the relationship between the allowance of a magnetic material sheet, and the fall amount of an antenna output, (b) is the illustration figure. (A) is a graph which shows the relationship between the distance from a core to a magnetic material sheet, and the fall amount of an antenna output, (b) is the illustration figure. (A) is a schematic diagram showing the path of the magnetic field when the magnetic sheet is on the antenna unit side, (b) is a schematic diagram showing the path of the magnetic field when the magnetic sheet is on the metal side. The graph which shows the relationship between the number of coil turns, and the fall amount of antenna output. The graph which shows the relationship between the thickness of a magnetic material sheet, and the amount of reduction of antenna output. Schematic of a coil split type transmitter. (A) is a wave form diagram which shows the relationship between a coil gap and an inductance change rate, (b) is an illustration figure of each coil gap. (A) is a wave form diagram which shows the relationship between turns ratio and an inductance change rate, (b) is an illustration figure of each turns ratio.

Hereinafter, an embodiment of an antenna device embodying the present invention will be described with reference to FIGS.
As shown in FIG. 1, the vehicle 1 is provided with a key operation free system 3 that performs ID collation wirelessly with an electronic key 2 using communication from the vehicle 1 as a trigger. In this case, the vehicle 1 includes a key verification device 4 that performs ID verification with the electronic key 2, a door lock device 5 that manages the locking and unlocking operation of the vehicle door, and an engine starter 6 that manages the operation of the engine. These are provided and connected via a bus 7 in the vehicle.

  The key verification device 4 is provided with a verification ECU (Electronic Control Unit) 8 that controls the key verification device 4 in an integrated manner. The ID code of the electronic key 2 is registered in the verification ECU 8. The verification ECU 8 includes an in-vehicle transmitter 9 that transmits LF (Low Frequency) band radio waves to the outside of the vehicle, an in-vehicle transmitter 10 that transmits LF radio waves into the car, and a vehicle receiver 11 that receives UHF band radio waves. It is connected. The vehicle-side transmitter 9 and the vehicle-side transmitter 10 constitute an antenna device.

  When the vehicle 1 is in a parked state, the verification ECU 8 intermittently transmits a request signal Srq from the outside-vehicle transmitter 9 to execute smart communication (outside-vehicle smart communication). When the electronic key 2 enters the outside communication area of the request signal Srq and the electronic key 2 receives the request signal Srq, the electronic key 2 is activated and transmits the ID signal Sid by UHF radio waves. The ID signal Sid includes an ID code registered in the electronic key 2. When the verification ECU 8 receives the ID signal Sid after transmitting the request signal Srq, it performs smart verification (external vehicle smart verification) as ID verification, and if this verification is established, permits or executes door lock locking / unlocking.

  When the user gets in the vehicle, the in-vehicle transmitter 10 starts transmission of the request signal Srq instead of the previous out-of-vehicle transmitter 9 and executes smart communication (in-vehicle smart communication). Smart collation (in-car smart collation) similar to that outside the vehicle is performed inside the vehicle, and if this collation is established, operation of power supply transition and engine start by the push momentary engine switch 12 installed in the vehicle is permitted.

  2 to 4 show the structure of the outside transmitter 9. Since the in-vehicle transmitter 10 has the same structure as the out-of-vehicle transmitter 9, only the out-of-vehicle transmitter 9 will be described here. The outside transmitter 9 is provided with a case 13 for storing various parts of the outside transmitter 9. The case 13 has a long and thin hollow box shape and is made of resin. The out-of-vehicle transmitter 9 is assembled to a vehicle body (metal 14) such as a vehicle door with screws or the like. The metal 14 is made of, for example, an iron plate that forms a vehicle body. The metal 14 corresponds to the antenna device installation location.

  As shown in FIG. 2, an antenna unit 15 of the outside transmitter 9 is housed inside the case 13. The antenna unit 15 includes a rod-shaped core 16 made of a material with high magnetic permeability (for example, ferrite), and a coil 17 formed by winding a plurality of antenna wires (electric wires) around the core 16. The coil 17 is wound around, for example, a bobbin (not shown) and is in an attached state in which the core 16 is inserted into the bobbin. The antenna unit 15 is formed of a series resonance circuit in which the coil 17 is L (inductance) and the capacitor of the substrate provided in the outside transmitter 9 is C (capacitance).

  As shown in FIGS. 2 and 4, a magnetic sheet 18 that suppresses a decrease in the electric field strength of the antenna is attached to the back surface of the case 13. The magnetic material sheet 18 is made of a sheet made of, for example, iron oxide, ferrite, cobalt, or the like and formed into a rectangular band shape. As shown in FIG. 4, the magnetic sheet 18 is formed so as to have a larger area than the antenna unit 15 in plan view. The magnetic material sheet 18 prevents the electric field component radiated from the antenna as a radio wave from reaching the metal 14 of the vehicle body, thereby suppressing a decrease in electric field strength.

Next, the effect | action of the magnetic material sheet 18 of this example is demonstrated using FIG. 2, FIG.
As shown in FIG. 2, when the magnetic material sheet 18 is disposed between the metal 14 and the antenna unit 15, a large number of magnetic fields of the antenna unit 15 pass through the magnetic material sheet 18. It is possible to suppress the reaching magnetic field to be small. Therefore, since the amount of eddy current generated in the metal 14 can be suppressed to a low level, the disappearance of the magnetic field caused by the eddy current is reduced. Therefore, the metal influence of the antenna unit 15 can be reduced, and the effect of securing the electric field strength is enhanced.

  FIG. 5 shows the relationship between the allowance L of the magnetic material sheet 18 and the amount of decrease in the antenna output. The margin L is from the end of the coil 17 in the axial direction (X-axis direction in FIG. 5: coil axial direction) and the longitudinal direction of the magnetic sheet 18 (X-axis direction in FIG. 5: sheet longitudinal direction). It is the length to the edge part. Moreover, the magnetic material sheet 18 is set to the same allowance L on both sides in the sheet longitudinal direction. However, the allowance L is not limited to the same length on the left and right, and may be different. In addition, the allowance L is equivalent to the length of the magnetic material sheet 18 extended in the coil axial direction from the coil end.

  As shown in the figure, it can be seen that the amount of decrease in the antenna output improves as the allowance L increases. In other words, it can be understood that as the output allowance L increases, the decrease in the electric field strength of the antenna can be suppressed. Therefore, it is effective to make the allowance L as large as possible so as to protrude from the coil 17. However, it is not preferable that the magnetic sheet 18 becomes too large. Therefore, the allowance L in this example is set to, for example, 8 mm to 30 mm in consideration of the balance between the value of the reduction amount of the antenna output and the size of the magnetic material sheet 18.

  FIG. 6 shows the relationship between the distance R1 from the core 16 to the magnetic sheet 18 and the amount of decrease in antenna output. In the characteristic diagram of FIG. 6, the distance between the core 16 and the metal 14 in the height direction (Z-axis direction in FIG. 6) is constant, and the core 16 to the magnetic sheet 18 are within this constant distance. The ratio between the distance R1 and the distance R2 from the magnetic sheet 18 to the metal 14 is changed. As shown in the figure, it can be seen that as the distance R1 from the core 16 to the magnetic sheet 18 increases, the amount of decrease in the antenna output is improved. That is, it can be seen that the closer the magnetic sheet 18 is to the metal 14, the more the decrease in the electric field strength of the antenna can be suppressed.

  FIG. 7 shows this principle. As shown in FIG. 7A, when the magnetic sheet 18 is on the antenna unit 15 side, there is a space between the metal 14 and the magnetic sheet 18, so that the antenna unit There is a current situation in which the area where the magnetic field (magnetic flux) of 15 wraps around the metal 14 side increases. Therefore, the eddy current generated in the metal 14 increases and the magnetic field is canceled. For this reason, the energy of the magnetic field is lost, and as a result, the electric field strength is greatly reduced. On the other hand, as shown in FIG. 7B, when the magnetic sheet 18 is on the metal 14 side, there is no space (gap) between the metal 14 and the magnetic sheet 18, so a magnetic field (magnetic flux) is present here. A magnetic field (magnetic flux) that does not wrap around and collides with the metal 14 is only at a location outside the magnetic material sheet 18. Therefore, the eddy current generated in the metal 14 can be reduced, and the amount of magnetic field to be canceled can be reduced. For this reason, there is little energy loss of a magnetic field, and it is thought that suppression of electric field strength can be reduced as a result. Therefore, the magnetic sheet 18 of this example is brought into close contact with the metal 14 so that the distance R2 from the magnetic sheet 18 to the metal 14 is set to zero.

  FIG. 8 shows the relationship between the thickness W of the magnetic sheet 18 and the reduction amount of the antenna output. As shown in the figure, it can be seen that as the thickness W of the magnetic sheet 18 is increased, the amount of decrease in the antenna output is improved. Therefore, it is preferable to increase the thickness W of the magnetic material sheet 18 to such an extent that the size of the outside transmitter 9 does not increase.

  FIG. 9 shows the relationship between the number of turns (number of turns) N of the coil 17 and the amount of decrease in antenna output. As shown in the figure, it can be seen that the amount of decrease in antenna output is improved as the number N of coil turns increases. Therefore, it is preferable to increase the number N of coil turns as much as possible.

  By the way, when the magnetic sheet 18 is provided between the metal 14 and the antenna unit 15, the amount of eddy current generated in the metal 14 can be suppressed, but one component of the magnetic field is consumed by the magnetic sheet 18. There is also a desire to increase antenna efficiency. Therefore, in this case, as shown in FIG. 10, the coil 17 is divided into a first divided coil 17a and a second divided coil 17b. As described above, when the coil 17 is divided, a space for further winding the winding is formed, which leads to an advantage that the number N of turns of the coil 17 can be increased. In order to increase the number of coil turns N, in addition to dividing the coil 17, for example, it is possible to increase the space between the windings of the coil 17, that is, to wind the coil 17 with a sufficient winding width. . The first divided coil 17a and the second divided coil 17b constitute a divided winding.

  Here, it is known that the resonance frequency fc of the antenna is obtained by the following equation, where L is the inductance of the series resonance circuit and C is the capacitance.

よって、アンテナのインダクタンスを調整すれば、結果として、共振周波数ｆｃを所望の値に切り換えることが可能である。

Therefore, if the inductance of the antenna is adjusted, as a result, the resonance frequency fc can be switched to a desired value.

  FIG. 11 shows the relationship between the coil gap T when the coil 17 is divided and the inductance change rate. In this example, the left side of the drawing is the first divided coil 17a, the right side of the drawing is the second divided coil 17b, and the interval between the first divided coil 17a and the second divided coil 17b is the coil gap T.

  As shown in the figure, it can be seen that as the coil gap T increases, the inductance change rate increases. Accordingly, when it is desired to switch the resonance frequency fc with a small value, the coil gap T is set to be small, while when it is desired to switch the resonance frequency fc to be large, the coil gap T is set to be large.

  FIG. 12 shows the relationship between the turn ratio M of the first divided coil 17a and the second divided coil 17b and the inductance change rate. As shown in the figure, it can be seen that as the turn ratio M increases, the inductance change rate increases. Therefore, when it is desired to switch the resonance frequency fc with a fine value, the turn ratio M is set to be small, while when it is desired to switch the resonance frequency fc to be large, the turn ratio M is set to be large.

  As described above, in this example, since the magnetic sheet 18 is disposed between the metal 14 and the antenna unit 15, the magnetic field of the antenna unit 15 can be actively guided to the magnetic sheet 18. Therefore, the magnetic field component from the antenna unit 15 to the metal 14 can be suppressed to a low level, and the eddy current generated in the metal 14 can be suppressed to a low level. For this reason, since the electric field strength fall caused by eddy current is suppressed to a small extent, the effect of securing the electric field strength of the antenna unit 15 is enhanced.

  Moreover, since the allowance L of the magnetic material sheet 18 is set to a value of 8 to 30 mm, as can be seen from the experimental results, the magnetic material sheet 18 is not unnecessarily increased in size while suppressing the decrease in the electric field strength. That's it. Therefore, it is possible to achieve both the electric field strength of the magnetic sheet 18 and the size reduction of the antenna. Further, in this example, the distance from the core 16 to the magnetic sheet 18, the number N of turns of the coil 17, the thickness W of the magnetic sheet 18 and the like can be set to suitable values derived from the experimental results. It is also possible to effectively suppress the electric field strength decrease.

  Furthermore, if the coil 17 is divided (the first divided coil 17a and the second divided coil 17b), it is possible to further wrap the antenna wire around the open space, so that the number of coil turns N can be increased accordingly. . Therefore, when the magnetic sheet 18 is provided for the purpose of preventing the generation of eddy currents, a magnetic field component that is absorbed by the magnetic sheet 18 itself comes out, but this absorbed magnetic field component is complemented by an increase in the number of turns. Therefore, the antenna efficiency can be improved.

According to the configuration of the present embodiment, the following effects can be obtained.
(1) Since the magnetic sheet 18 is disposed between the antenna unit 15 and the metal 14, magnetic field loss due to eddy current is reduced, and the electric field strength of the antenna unit 15 can be ensured. Moreover, since the allowance L of the magnetic material sheet 18 is set to 8 to 30 mm, it is possible to achieve both suppression of electric field strength reduction and prevention of size increase.

  (2) Since the magnetic sheet 18 is arranged on the metal 14 side in the height direction (Z-axis direction), the magnetic field output from the antenna unit 15 has many components passing between the antenna unit 15 and the magnetic sheet 18. On the other hand, a component passing between the magnetic sheet 18 and the metal 14 is reduced. Accordingly, the effect of preventing the generation of eddy currents in the metal 14 is enhanced, and as a result, the reduction in electric field strength is suppressed.

  (3) If the allowance L, the distances R1, R2, the thickness W, and the number N of coil turns are set to suitable values that can be understood from the experimental results, the vehicle-side transmitter 9 and the vehicle-mounted transmitter 10 are preferably It can be an antenna.

  (4) When the coil 17 is divided, the antenna wire can be further wound around the space formed thereby to increase the number N of coil turns. Therefore, even if an electric field loss occurs in the magnetic sheet 18 itself, it can be supplemented by this increase in the number of turns.

  (5) Since the magnetic material sheet 18 is affixed to the back surface of the case 13, these can be made into one unit component. Therefore, it is possible to facilitate the handling of the outside transmitter 9 and the inside transmitter 10.

Note that the embodiment is not limited to the configuration described so far, and may be modified as follows.
-The allowance L may take any value as long as it is a value within the range of 8 to 30 mm.
The coil gap T and the coil turn number N can be changed as appropriate according to the required electric field strength. The same applies to other parameters related to antenna output and resonance frequency.

The resonance circuit is not limited to a series resonance circuit, and may be a parallel resonance circuit.
The magnetic sheet 18 is not limited to having a larger area than the antenna unit 15, that is, the component in which the core 16 and the coil 17 are integrated in a plan view. In short, it is sufficient that the magnetic sheet 18 is larger than the coil 17 in the coil axial direction.

The magnetic material sheet 18 is not limited to being disposed on the metal 14 side in the height direction, and the height position can be changed as appropriate.
The magnetic sheet 18 is not limited to being attached to the case 13 and may be disposed between the antenna unit 15 and the metal 14.

-A magnetic body is not limited to a sheet-like member, You may employ | adopt another shape. The magnetic sheet 18 is not limited to a rectangular shape, and other shapes such as a perfect circle and a regular square can be adopted.
The antenna device is not limited to a bar antenna, and other antenna types can be used.

-When making the coil 17 into a division type, it is not limited to dividing into two, and it is good also as three or more.
The antenna device installation location is not limited to the vehicle body, and any metal 14 may be used.

The antenna device is not limited to being applied to both the in-vehicle transmitter 9 and the in-vehicle transmitter 10, and may be applied to only one of them.
-An antenna apparatus is not limited to a vehicle antenna, You may apply to another apparatus and apparatus.

Next, technical ideas that can be grasped from the above-described embodiment and other examples will be described below together with their effects.
(A) In any one of claims 1 to 4, the magnetic body is formed in a sheet shape and has a larger area than the antenna unit in a plan view. According to this configuration, since the magnetic body has a sufficient size, the effect of securing the electric field strength is enhanced.

  (B) In any one of claims 1 to 4 and the technical idea (A), the length is set to a length of 8 to 25 mm, 8 to 20 mm, 8 to 15 mm, and 10 to 15 mm. . According to this configuration, a desired electric field decrease suppressing effect can be obtained by setting the separation length to an appropriate distance.

  DESCRIPTION OF SYMBOLS 9 ... Outside transmitter which comprises antenna apparatus, 10 ... In-vehicle transmitter which comprises antenna apparatus, 13 ... Case, 14 ... Metal as antenna apparatus installation place, 15 ... Antenna unit, 16 ... Core, 17 ... Coil, 17a A first divided coil constituting a divided winding, 17b a second divided coil constituting a divided winding, 18 a magnetic sheet as a magnetic material, L a length as a margin, and N a number of turns.

Claims (4)

In an antenna device in which an antenna wire is wound around a core with high permeability and the annular antenna wire becomes a coil of a resonance circuit,
A magnetic body capable of absorbing the magnetic field radiated from the coil is provided between the coil and the antenna device installation place, and the total length of the magnetic body in the axial direction of the coil is 8 to 8 mm from each end of the coil. An antenna device characterized by being set to a length of 30 mm apart. The antenna device according to claim 1, wherein the magnetic body is disposed on the antenna device installation location side between the coil and the antenna device installation location. The coil is a divided winding in which the group of antenna wires is divided into a main winding and an auxiliary winding, and the number of turns of the coil is increased by further winding the antenna wire in a space formed by the division. The antenna device according to claim 1, wherein the antenna device is provided. An antenna unit comprising at least the coil;
A case for storing the antenna unit;
The antenna device according to claim 1, wherein the magnetic body is attached to a back surface of the case.

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